Here is my latest build an Ultra Linear / Triode Mode KT66 / KT88/6550 . ( the AirTight M101 clone when KT88 / 6550 installed )
Output transformers used in the past projects are Hashimoto ,Tamura , Electra Print , Finemet , Amorphous , Grain Orientated Steel both EI and C cores M6, M4 and M3 often called HiB and Super HiB
After many builds including Single Ended 45 , 2a3 , 300B, PX4 , EL84 , EL509 and now launching into KT66 and KT88/6550 both Ultra Linear and Triode strapped .
My latest build was inspired by the now obsolete AirTight M101 Kitset Single Ended KT88 .
I saw a number of pictures on the net including under the Chassis and pretty much reverse engineered the circuit , quite a simple affair of 12AX7 plates strapped togeather and a KT88 biased with a 600ohm cathode resistor starting with the premise of a B+ rail of 400v DC .
It looked as though the 12AX7 input tube with plates / grids and cathodes strapped together was biased at about 1.3mA , I lifted mine to 2mA .
I first tried the Amplifier with a power transformer B+ 400v output and B+ 385v under load with a SE KT66 triode Plate 373V bias -43 V 63mA 470R Cathode Resistor and Ultral Linear at 70mA Plate 363v bias -27V 380 ohm Cathode R , always seems the tubes don't bias up exactly to publish data !!
The KT66 was first designed back in 1937 by MOV in the UK for Audio Used from its inception to work both in Kinkless Tetrode and Strapped in Triode from day one .
With the latest Muse Coils custom design for me a primary of 4.6K / 3.3K /2.25K / - 4 / 9 and 16 Ohms with %40 Ultra Linear tap for the 4.6K load 70mA max at 4.6K and 80mA at 3.3K / with UL tap
Model MinotauR OTSE - 060NHY-046 is the first Alexander had made of this model and very useful for experimenting with many tube types .
I also have a custom set of 4.3K 20 watt UL Single Ended transformers from https://www.thermioniclab.com/ and a new set of Tamura F915 with a UL tap which
I will also try in the Amplifier also ,the Tamura would be a much closer clone to the original AirTight M101 sound .
The Triode KT66 after the run in period was very pleasing indeed as MOV designed this tube in triode to emulate the highly regarded PX25 directly heated triode the British answer to the 300B .
In triode mode the sound had excellent transparency , full and extended bass and high frequencies , the midrange had all the qualities of a 2A3 but nearly twice the power at 5.8 watts .
The overall impression was excellent with Muse Coils transformer s( https://musecoils.com/?bot_test=1) , Single HiB cut C core with double coils similar design to Lundahl and the best Japanese Nogushi and the Tamura F2007 .
In Ultra Linear at 7.2 watts the KT66 exhibited more bass slam and high frequency dominance , the midrange was neutral but to match the 2A3 I will remove the Jupiter Copper Foil capacitor and replace with a Toshin DUCT Paper in Oil Vita Q capacitor from the Hifi Collective UK to get more of the AM101 original sound .
Next after this will be the GE KT88 / 6550 although labelled GE KT88 it looks certainly to be a 6550 which is a highly regarded NOS GE tube .
The 12AX7 I decided to use was a NOS Japanese Toshiba 12AD7 the very low noise closely matched version the the 12AX7 with very close matched plates suitable for strapping together .
All my signal wiring is point to point copper foil at present and resistors I have chosen are mainly Amtram AMRT carbon resistors and capacitors from mainly Vishay Sprague ATOM and a full bridge rectifier using HEXFREDs bypassed with 0.01 uf 1200v ceramic capacitors .
The LM317 has been replaced with wire wound resistors .
NOW are few pictures of the chassis and woodwork ( almost finished ) to be fitted and Muse Coil Transformer Plots 15Hz - 52Khz -1dB 1K driving impedance
Output transformers used in the past projects are Hashimoto ,Tamura , Electra Print , Finemet , Amorphous , Grain Orientated Steel both EI and C cores M6, M4 and M3 often called HiB and Super HiB
After many builds including Single Ended 45 , 2a3 , 300B, PX4 , EL84 , EL509 and now launching into KT66 and KT88/6550 both Ultra Linear and Triode strapped .
My latest build was inspired by the now obsolete AirTight M101 Kitset Single Ended KT88 .
I saw a number of pictures on the net including under the Chassis and pretty much reverse engineered the circuit , quite a simple affair of 12AX7 plates strapped togeather and a KT88 biased with a 600ohm cathode resistor starting with the premise of a B+ rail of 400v DC .
It looked as though the 12AX7 input tube with plates / grids and cathodes strapped together was biased at about 1.3mA , I lifted mine to 2mA .
I first tried the Amplifier with a power transformer B+ 400v output and B+ 385v under load with a SE KT66 triode Plate 373V bias -43 V 63mA 470R Cathode Resistor and Ultral Linear at 70mA Plate 363v bias -27V 380 ohm Cathode R , always seems the tubes don't bias up exactly to publish data !!
The KT66 was first designed back in 1937 by MOV in the UK for Audio Used from its inception to work both in Kinkless Tetrode and Strapped in Triode from day one .
With the latest Muse Coils custom design for me a primary of 4.6K / 3.3K /2.25K / - 4 / 9 and 16 Ohms with %40 Ultra Linear tap for the 4.6K load 70mA max at 4.6K and 80mA at 3.3K / with UL tap
Model MinotauR OTSE - 060NHY-046 is the first Alexander had made of this model and very useful for experimenting with many tube types .
I also have a custom set of 4.3K 20 watt UL Single Ended transformers from https://www.thermioniclab.com/ and a new set of Tamura F915 with a UL tap which
I will also try in the Amplifier also ,the Tamura would be a much closer clone to the original AirTight M101 sound .
The Triode KT66 after the run in period was very pleasing indeed as MOV designed this tube in triode to emulate the highly regarded PX25 directly heated triode the British answer to the 300B .
In triode mode the sound had excellent transparency , full and extended bass and high frequencies , the midrange had all the qualities of a 2A3 but nearly twice the power at 5.8 watts .
The overall impression was excellent with Muse Coils transformer s( https://musecoils.com/?bot_test=1) , Single HiB cut C core with double coils similar design to Lundahl and the best Japanese Nogushi and the Tamura F2007 .
In Ultra Linear at 7.2 watts the KT66 exhibited more bass slam and high frequency dominance , the midrange was neutral but to match the 2A3 I will remove the Jupiter Copper Foil capacitor and replace with a Toshin DUCT Paper in Oil Vita Q capacitor from the Hifi Collective UK to get more of the AM101 original sound .
Next after this will be the GE KT88 / 6550 although labelled GE KT88 it looks certainly to be a 6550 which is a highly regarded NOS GE tube .
The 12AX7 I decided to use was a NOS Japanese Toshiba 12AD7 the very low noise closely matched version the the 12AX7 with very close matched plates suitable for strapping together .
All my signal wiring is point to point copper foil at present and resistors I have chosen are mainly Amtram AMRT carbon resistors and capacitors from mainly Vishay Sprague ATOM and a full bridge rectifier using HEXFREDs bypassed with 0.01 uf 1200v ceramic capacitors .
The LM317 has been replaced with wire wound resistors .
NOW are few pictures of the chassis and woodwork ( almost finished ) to be fitted and Muse Coil Transformer Plots 15Hz - 52Khz -1dB 1K driving impedance
Attachments
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Hi, Am moving house so test gear and lost's of excess parts being boxed up , seeing it a 1K load on the test i expect 20Hz at -1dB easily and still well into the 40KHz range -1dB on the HF side .
Alexander at Muse Coils oversizes his C cores and very thorough in the manufacturing design phase .
The KT66 in triode mode is very linear indeed .
Alexander at Muse Coils oversizes his C cores and very thorough in the manufacturing design phase .
The KT66 in triode mode is very linear indeed .
Attachments
Sounds encouraging, and the transformers look beautiful. But it would be interesting to see actual measurements when you are able.